1. Field of the Invention
This invention relates to hydrocyclones, and more particularly to a hydrocyclone having an unconstrained tube or rod serving as a vortex breaker within the hydrocyclone body.
2. Description of Related Art
A cyclone is a device commonly used to separate entrained solids from liquids or gases, or to classify entrained solids into lower and higher density fractions. In the usual application, a carrier fluid (gas or liquid), containing solid particles of varying densities greater than the fluid density, enters the vertical body of a cyclone under pressure through a horizontal tangential inlet located near the top. The energy of the entering suspension is converted to rotation within the body of the cyclone. The different density components stratify under centrifugal force. Carrier fluid, containing most of the higher density solid particles, is discharged at the apex located at the bottom end of the cyclone body, and the remainder of the carrier fluid, also containing lower density solid particles, is discharged through a “vortex finder” tube protruding through the center of the top end near the tangential inlet and terminating below the invert of the tangential inlet. When the fluid is water or other liquid, the term hydrocyclone is frequently used to describe such a device. Besides the usual application of classifying suspensions of particulate matter in liquids, hydrocyclones have also found application in separation of non-emulsified oils from water, where the oil is only slightly less dense than water.
In the operation of a hydrocyclone, an outer vortex or helical flow pattern containing dense particles (or, in the case of oil-water separation, the water phase) progresses from the inlet end towards the apex end, while concurrently an inner vortex or helical flow pattern concentric with the outer vortex containing mostly carrier liquid with lower-density material (or, in the case of oil-water separation, the oil phase) progresses in the opposite direction, towards the vortex finder. An air core forms within the inner vortex in the vacuum occurring at or near the center longitudinal axis, starting at the apex and extending upwards. The maintenance and control of the outer and inner vortices, and the air core, is important to the function of hydrocyclones in classifying or separating entrained material of a density greater than or slightly less than that of the carrier liquid, where the higher-density material is concentrated in the flow leaving the apex.
Hydrocyclones almost always are designed with a tapered body, where higher and higher centrifugal forces develop as the rotating mass is displaced downward within the body, because unacceptably low separation efficiencies result if the body is cylindrical. Numerous means have been devised to increase the efficiency of separation of dense particulates from the carrier fluid in tapered body hydrocyclones, such as the elongate core extending downward from the vortex finder described in U.S. Pat. No. 6,024,874 dated Feb. 15, 2000, the adjustable flow restrictor within the vortex finder described in U.S. Pat. No. 3,568,847 dated Mar. 9, 1971, and the dewatering tube extending upwards from the apex described in U.S. Pat. No. 4,786,412 dated Nov. 22, 1988. Hydrocyclones are most commonly installed vertically, with the tangential inlet and vortex finder at the top, although in some applications the angle from the vertical varies up to 90 degrees.
Stabilized emulsions of gases in liquids (usually air in water) are useful in industrial separation processes, cleaning of textiles and surfaces, fire suppression, and other applications. The gas phase of such emulsions is comprised of a very large number of fine bubbles in the size range of 5 to 100 microns, each bubble coated with a film of surfactant to prevent immediate coalescence of the bubbles. The fluid properties of stabilized air-water emulsions are unusual, in that the bulk density is between 30% and 80% of the density of water, yet the viscosity is very nearly equal to that of water. When producing these emulsions in a recycle type generator, it has been found necessary to classify a stream of emulsion into fractions of lower and higher bulk densities in order to obtain the desired emulsion quality.
The literature has almost no references relating to the use of hydrocyclones for classifying suspensions or emulsions of gases in liquids, although laboratory bench scale continuous air-water emulsion generators using two small tapered-body hydrocyclones in series are known to be able to classify a stabilized gas-liquid emulsion into two fractions of different bulk densities, where the emulsified material (air) is far less dense than the carrier fluid (water). The hydrodynamics of this kind of two-phase system in hydrocyclones is not well understood. In operation, pressurized recycled air-water emulsion stabilized with a surfactant enters the tangential inlet of the first hydrocyclone. The lower bulk density emulsion fraction issues under pressure through the top (vortex finder) outlet of the first hydrocyclone, while the higher bulk density emulsion fraction is ejected out of the apex. The emulsion product from the first hydrocyclone is further classified by introducing it into the tangential inlet of a second hydrocyclone. Emulsion product of still lower bulk density, of suitable quality for experimental use, issues under pressure from the top (vortex finder) outlet of the second hydrocyclone while a relatively denser emulsion fraction is ejected out of the apex. The maximum possible rate of production of stabilized air-water emulsion using this type of apparatus is less than 1.3 gallons per minute.
Numerous attempts at simple scaleup of hydrocyclone classifiers for gas-liquid emulsions have heretofore proven unsuccessful beyond a production rate of about 2 gallons per minute of emulsion, due to the inoperability of hydrocyclones larger in inside diameter than about ¾ inches in this application. The inventor found by experimentation, using either commercially available tapered body hydrocyclones or custom-built cylindrical bodied hydrocyclones with various combinations of dimensions, that for hydrocyclone body diameters greater than ¾ inch and inlet emulsion flow rates greater than about 5 gallons per minute, greater bulk density emulsion issued from the vortex finder at the upper end and lesser bulk density emulsion issued from the apex. The inventor observed that the fluid rotating within the lower portion of the hydrocyclone was of lesser density than the average density throughout the entire volume of the hydrocyclone, apparently due to the entry of excess air through the apex countercurrent to the flow of emulsion out the apex, and concluded that this was why lesser-density emulsion was observed discharging from the apex. This was the reverse of the desired action, and prevented the generation of acceptable quality emulsion.